Polysilicon surface micromachining adapts planar fabrication process steps known to the integrated circuit (IC) industry to manufacture microelectromechanical or micromechanical devices. The standard building-block processes for polysilicon surface micromachining are deposition and photolithographic patterning of alternate layers of low-stress polycrystalline silicon (also termed polysilicon) and a sacrificial material (e.g. silicon dioxide or a silicate glass). Vias etched through the sacrificial layers at predetermined locations provide anchor points to a substrate and for mechanical and electrical interconnections between the polysilicon layers. Functional elements of the device are built up layer by layer using a series of deposition and patterning process steps. After the device structure is completed, it can be released for movement by removing the sacrificial material in part or entirely by exposure to a selective etchant such as hydrofluoric acid (HF) which does not substantially attack the polysilicon layers.
The result is a construction system that generally consists of a first layer of polysilicon which provides electrical interconnections and/or a voltage reference plane (e.g. a ground plane), and up to three or more additional layers of mechanical polysilicon which can be used to form functional elements ranging from simple cantilevered beams to complex systems such as a microengine connected to a gear train. Typical in-plane lateral dimensions of the functional elements can range from one micron to several hundred microns or more, while individual layer thicknesses are typically about 1-3 microns. Because the entire process is based on standard IC fabrication technology, a large number of fully-assembled devices can be batch-fabricated on a silicon substrate without any need for piece-part assembly.
For various types of microelectromechanical (MEM) devices, a precise control over movement, positioning or timing of a plurality of rotary members is needed. Such precise movement, positioning or timing control has previously been achieved using a gear train. However, gear trains require precise fabrication and are limited in their utility when the rotary members are widely spaced, or when a plurality of rotary members at different locations must be driven at the same angular speed.
An advantage of the present invention is that a surface-micromachined chain can be integrally formed on a substrate and used to simultaneously drive one or more rotary members (e.g. sprockets) that are located at a distance from a motive source (e.g. a microengine).
Another advantage is that the surface-micromachined chain of the present invention allows a single motive source (e.g. a microengine) to drive a plurality of rotary members (e.g. sprockets) in synchronism.
Yet another advantage of the present invention is that the surface-micromachined chain can be used to combine the mechanical power from a plurality of motive sources.
A further advantage of the present invention is that the surface-micromachined chain can be formed in place on a substrate without any piece-part assembly required.
These and other advantages of the method of the present invention will become evident to those skilled in the art.